| 1. |
- Sonesten, Lars, et al.
(författare)
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Uncertainty in nutrient loads resulting from discharge data uncertainty
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Reliable estimates of nutrient loads discharged to the sea are important for managing marine and upstream water resources. Most major river mouths in Sweden are monitored for discharge and nutrient concentrations. These data are used together with direct point source loads as the basis for annual load estimates. The estimates are used as a basis for national environmental policy and they are reported to international bodies such as the EEA (SoE TCM report), OSPAR (OSPAR RID report) and HELCOM (PLC-Annual report). The Pollution Load Compilation-Annual (PLC-Annual) report to HELCOM is used as evidence for managing eutrophication in the Baltic Sea. The reliability of load estimates based on monitoring data in gauged catchments is affected by uncertainty in the discharge and nutrient concentration data. Knowledge about the uncertainty associated with the load estimate values is of fundamental importance when using these data as a basis for management decisions, e.g. for assessing fulfillment of national environmental objectives, or analysing trends in the loads over time (i.e. is it a real change that is observed or is it a result of data uncertainty?). In the PLC-Annual reports for 2015 and onwards both the loads and the estimated uncertainty in the loads should be reported. The aim of this study was to quantify uncertainty in discharge data resulting from rating curve uncertainty and its impact on uncertainty in the nitrogen and phosphorous PLC-Annual load estimates at selected river mouths. In total there are 34 river mouth stations for which the PLC-Annual load calculations are based entirely on measured discharge (i.e. no modelled data are used). We used data from the 12 river mouth stations that are run by the Swedish Meteorological and Hydrological Institute, SMHI, for which data were available to estimate discharge uncertainty. These stations are representative of all the 34 stations in terms of catchment characteristics except for a lower degree of river regulation. Discharge was calculated indirectly from water level (stage) at all these stations using a rating curve, which is fitted to stage–discharge gaugings. For each discharge station we used 15-minute water-level data for 2005–2014 and the stage–discharge gaugings that had been used to fit the current rating curve equation. Rating curve uncertainty was estimated with the Voting Point likelihood method in a Monte Carlo analysis, essentially estimating multiple feasible rating-curve parameter sets that are compatible with the uncertain gauging data. We estimated 40,000 rating curves and the method succeeded in 5 capturing the uncertainty in the gauging data at all stations. Only a few of the stations had extrapolated rating curves during the time period and most of the stations had a well constrained rating curve uncertainty for the mid and high flow range. For each rating curve a time series of discharge was calculated from the stage time series and aggregated to daily values. The 90% uncertainty interval for the relative uncertainty in the daily flow percentiles was around ±15–50% for low flows (Q95, i.e. the flow exceeded 95% of the time), ±10% for mean flow, and around ±10–25% for high flows (Q0.1 and Q0.01). These estimates include both model and data error, which means that they are likely conservative estimates. Rating curves are normally updated continuously as new data become available. Effects of historic rating curve updates were visible in the official discharge time series for some of the stations (as differences in comparison to the PLC-Annual discharge data). These differences were of a similar magnitude as the 90% uncertainty interval from the rating-curve uncertainty estimated here. The uncertainties we estimated from the gauging data were therefore representative of those stemming from real rating-curve changes in the last 10 years. The nutrient load uncertainty was estimated by repeating the PLC-Annual load calculation method (interpolation of monthly nutrient concentrations to daily values that are then multiplied by discharge) for each estimated discharge time series. As a result of the rating curve uncertainty, the estimated relative uncertainty in the PLC-Annual nitrogen and phosphorous loads was ±7–14% (the half-widths of the 90% interval). However, there were biased uncertainty distributions up to ±30–40% for individual years as a result of errors in the water-level time series (that had been updated after the data was delivered for the load calculations). We therefore recommend that the historic load estimates are updated regularly in the future to take advantage of successive data quality improvements. The potential impact of load uncertainty should be considered when load estimates are used for other analyses or as a basis for policy decisions. We expect a greater impact on load comparisons between catchments compared to between sea basins, and for individual years compared to long-term averages. Trend analyses are expected to be obscured where the magnitude of the uncertainty is large in relation to the strength of the measured trend. This study has quantified the uncertainty arising from discharge data and has established an uncertainty estimation method that can be extended to include other components of the total load uncertainty. We recommend that future studies build on the current method to include uncertainty
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| 2. |
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| 3. |
- Sonesten, Lars, et al.
(författare)
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Vattenkvaliten i Vänerns tillflöden och utlopp
- 2016
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Ingår i: Vänern : årsskrift från Vänerns vattenvårdsförbund. ; 96, s. 50-59
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- De flesta av Vänerns tillflöden uppvisade en något högre vattenföring under året än normalt, vilket framförallt beror på att året överlag var jämförelsevis nederbördsrikt. Den något förhöjda vattenföringen innebar även att transporterna av näringsämnen i vattendrag var något förhöjda. Halterna av kväve och fosfor var överlag på normala nivåer, även om några vattendrag har uppvisat ökande halter under senare år. Halterna av organiskt material har under senare år stabiliserats eller i några fall till och med minskat efter en period med stadigt ökande halter.
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| 4. |
- Bringmark, Ewa, et al.
(författare)
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Long-term monitoring of scots pine litter decomposition rates throughout sweden indicates formation of a more recalcitrant litter in the south
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:8, s. 878-890
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition studies were carried out at sites throughout Sweden, including the four Integrated Monitoring sites. Scots pine needle litterbag weight loss measurements over 3 or 5 years were determined at 26 sites and repeated up to 27 times, depending on the site. Humus layer respiration rates were determined for 20 sites in 1987-1989 and repeated in 2007-2008. Partial Least Squares (PLS) regression was used to elucidate the relative importance of climatic and soil factors. Annual needle weight losses decreased only slowly (20-10%) over 3-5 years for all northern (> 60A degrees N) sites but decreased sharply from 30 to 10% in the third year in southern (< 60A degrees N) sites. Respiration rates of southern sites were less (40% on average) than those of northern sites. Humus layer N was positively correlated to needle weight loss during the first and the second years, but negatively correlated in the third year and to respiration rates. The results indicated that litter formed in southern Sweden became more recalcitrant in later stages of decomposition compared to litter produced in northern Sweden.
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| 5. |
- Eklöf, Karin, et al.
(författare)
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Spatial and temporal variation of THg concentrations in run-off water from 19 boreal catchments, 2000-2010
- 2012
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491 .- 1873-6424. ; 164, s. 102-109
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Tidskriftsartikel (refereegranskat)abstract
- Total mercury concentrations are presented for 19 Swedish watercourses 2000-2010, together with an analysis of factors affecting these concentrations in space and time. Organic matter (OM) measured as absorbance at 420 nm (Abs(420)) and total organic carbon (TOC) were the variables most strongly correlated with THg concentrations in the pooled dataset from all 19 watercourses, explaining 66% and 61% of the variance respectively. The correlation between THg and OM indicates that OM is the main controlling factor independent of geographical variation in Hg deposition, geology, or any other factor evaluated in this study. Despite an increase in TOC concentrations at most sites during the study period, THg increased in only one of the watercourses, and the THg/TOC ratio decreased significantly at six sites. The Abs(420) did not increase like TOC. We suggest that OM-fractions absorbing at 420 nm are more important for Hg mobilization than other OM-fractions.
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| 8. |
- Fölster, Jens, et al.
(författare)
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Åtgärder ger effekt
- 2012
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Ingår i: Havet 2012. - 9789198064612 ; , s. 33-34
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Quintana, Isabel, et al.
(författare)
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Vänern - Växtplankton
- 2011
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Ingår i: Rapport - Vänerns vattenvårdsförbund. - 1403-6134. ; , s. 35-38
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Quintana, Isabel, et al.
(författare)
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Växtplankton
- 2012
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Ingår i: Vänern – årsskrift 2012. ; :73, s. 40-43
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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